A PSC has a high efficiency in power conversion and a potential to achieve a low production cost, thus making the PSC a promising candidate as an energy harvester for sustainable energy source. Recent efforts of improving the PSC for commercialization include improving the power conversion efficiency (PCE), the scalability and manufacturability of the process as well. One problem is that in forming a top electrode on top of a perovskite layer of the solar cell, the top electrode is usually fabricated by a vacuum-based process, which is energy-consuming and costly. Developing printable electrode materials for the PSC using a solution-based process is therefore highly desirable.
There have been attempts to develop a carbon electrode formed by a conductive ink comprising, for example, metal oxide and graphite particles. The conductive ink can penetrate into the methylamine lead iodine mixed with zirconium dioxide as present in the perovskite layer to form the carbon electrode. However, this method involves high temperature annealing at 400-500° C. This high temperature annealing may result in a high cost and a long processing time in device fabrication. It may also affect the device performance.
Apart from directly mixing a carbon paste with the methylamine lead iodine, there have also been attempts of directly printing the conductive ink onto an interface layer of the cell. In this approach, the carbon electrode is formed after low-temperature annealing of the conductive ink (around 100° C., as disclosed by Kumar, M. H., et al. in “Flexible, low-temperature, solution processed ZnO-based perovskite solid state solar cells,” Chemical Communications, 2013, 49, pp. 11089-11091). Using the low temperature annealing is beneficiary for reducing the production cost. However, the solar cell fabricated using this low-temperature annealing approach results in a PCE that is relatively low (5%).
There is a need in the art for a technique of making a PSC with a carbon electrode formed based on printing and low-temperature annealing while improving the PCE of the solar cell.